Mechanistic Study of Cyclohexane Oxidation to KA Oil Enabled by Circulating Microdroplets

Conventional conversion of cyclohexane (CHA) to cyclohexanol and cyclohexanone (KA oil) requires special conditions involving high temperature, high pressure, complex catalysts, and long reaction time. This study elucidates efficient CHA oxidation to KA oil via an ultrasonic atomization microdroplet system with HCl and H₂O₂, identifying the microdroplet gas-liquid interface, rather than ultrasound, as the critical reaction milieu. Mass spectrometry (MS) and electron paramagnetic resonance (EPR) detection of cyclohexyl radical and •OH confirm a dominant interfacial free radical pathway initiated by •OH. Protons (H⁺) enhance interfacial •OH generation in water microdroplets while promoting H₂O₂ decomposition to •OH. The interfacial radical mechanism achieves 16.1% KA oil yield with 85% selectivity within 40 min and proves applicable to C5-C8 cycloalkanes. This work provides an environmentally benign alternative to conventional CHA oxidation while advancing fundamental knowledge of microdroplet-mediated interfacial C-H activation through radical mechanisms.